1. Field of the Invention
This invention relates to sound reproduction. More particularly, this invention relates to high fidelity loudspeaker systems of the motional-feedback type.
2. Prior Art
In my copending U.S. patent application Ser. No. 543,375 filed Oct. 19, 1983, there is disclosed a means for improving substantially the performance of high-fidelity loudspeaker systems. In accordance with that disclosure, which is incorporated herein by reference, such a result is achieved by feedback means including a small motion-sensing element, such as an accelerometer, mounted on the speaker coil. The output of that motion-sensing element is fed back negatively to the amplifier driving the coil, to assure that the loudspeaker motion faithfully tracks the sound signal.
Speakers manufactured in accordance with the teachings of that patent application have produced excellent results. However, it has been found that, particularly for low-frequency speaker systems such as "sub-woofers", improvements can be effected in several respects. Particularly, it has been found that low frequency stability of the feedback loop can be improved by sealing the shield can housing the motion-sensing element so as to form an air-tight enclosure for that element. Also high frequency stability can be enhanced by controlling acoustic effects in the cone-coil system in several ways, so as to de-tune the system.
Accordingly, it is a primary object of the present invention to provide a speaker of the motional feedback type with improved stability. Other objects, aspects, and advantages of the invention will in part be pointed out in, and in part apparent from, the following description considered together with the accompanying drawings.